In a communication network, especially a core network, high-speed and wideband communication has been developed. In many cases, an optical transmission network is used as a core network. For example, there is an Optical Transport Network (OTN), which is recommended by International Telecommunication Union (ITU), as a transmission specification of the optical transmission network. The OTN is given as an example to describe a frame that is transmitted and received on the communication network.
In the OTN, an overhead byte as a control signal is added to a signal, which flows into the optical transmission network, and is then transmitted as an OTN frame. The OTN frame includes an overhead of an Optical channel Payload Unit (OPU), and an overhead of an Optical channel Data Unit (ODU) in addition to a payload that stores a client signal. The overhead byte may be used to report a transmission quality and a state of the client signal to and from optical transmission devices.
The client signal may flow into the optical transmission network from various types of communication devices such as a packet communication device and a Synchronous Optical NETwork (SONET) device. In the OTN, various types of OTN frames are defined to store various types of client signals having different transmission rates. For example, a frame called an Optical channel Transport Unit (OTU) 1 may store a client signal of up to approximately 2.5 Gbps. An OTU 3 may store a client signal of up to approximately 40 Gbps. An OTU 4 may store a client signal of up to approximately 100 Gbps. As described above, the capacity of the OTN frame has been increased.
Regarding the communication system that performs communication in an ODU form specified by ITU G.709, Japanese Laid-open Patent Publication No. 2004-266480 discloses a technique for converting a signal form by adding a byte for control that includes a specific pattern to an original signal at a transmission side and for restoring an original signal at a reception side.